1. Field of the Invention
This invention generally relates to poly(ester amide) (PEA) polymer blends having a PEA polymer and a material or polymer capable of hydrogen-bonding with the PEA polymer, which have a glass transition temperature (Tg) higher than the PEA polymer and are useful for coating an implantable device such as a drug-delivery stent.
2. Description of the Background
Poly(ester amide) polymers are known for their relatively low glass transition temperatures. For example, co-poly-{[N,N′-sebacoyl-bis-(L-leucine)-1,6-hexylene diester]-[N,N′-sebacoyl-L-lysine benzyl ester]} (PEA-Bz) and co-poly{[N,N′-sebacoyl-bis-(L-leucine)-1,6-hexylene diester]-[N,N′-sebacoyl-L-lysine 4-amino-TEMPO amide]} (PEA-TEMPO) have a Tg of approximately 23° C. and 33° C., respectively.
Complications related to low Tg manifest themselves as reduced release rate control, potential sticking and adhesion to the delivery balloon, and reduced shelf life stability. Low Tg materials have higher drug permeabilities, which necessitates the use of greater amounts of polymer to control release rate of the drug. Moreover, the low Tg can enable the drug to diffuse within the coating. In other words, the drug configuration within a given coating can change with time until an equilibrium state is reached, resulting in release rate shifts. Low Tg materials also tend to be softer, they can be more adhesive to balloons, and are more prone to failure during mechanical perturbations such as crimping and expansion.
The embodiments of the present invention provide for methods addressing these issues.